Performance Evaluation of an Improved Unglazed Photovoltaic and Thermal Hybrid System

This paper proposes a novel unglazed photovoltaic/thermal (PV/T) system completely covered by photovoltaic (PV) cells, the system can significantly increase the power generation, and unglazed structure helps to improve the performance of the electricity. The variable flow experiment shows that the average value of the unglazed PV/T daily electrical and thermal efficiencies can reach 18.62% and 26.86%, respectively, and the corresponding exergy and energy saving efficiencies are 20.51% and 73.76%. Compared with PV module, the electrical efficiency of the PV/T module is increased by 11.54%. As for the large heat loss of unglazed PV/T, a series or parallel system composed of PV/T modules was built to improve heat collection capacity. The results show that the electrical and thermal energy of the series or parallel system increases significantly; temperature of water can be increased by 20 °C when the water volume is more than doubled. However, the electrical efficiency of the system is lower than that of the single PV/T, and the maximum value is 17.32%. Combined with economic analysis, the unglazed PV/T system with higher exergy efficiency and the cost is lower than that of glazed PV/T.